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Author ORCID Identifier

https://orcid.org/0000-0002-8127-0293

AccessType

Campus-Only Access for Five (5) Years

Document Type

dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Environmental Conservation

Year Degree Awarded

2021

Month Degree Awarded

September

First Advisor

Baoshan Xing

Abstract

Copper (Cu)-based pesticides have been widely used as a broad-spectrum

management strategy in agriculture over the past century. However, extensive

applications of conventional Cu-based pesticides over years can lead to Cu pollution and

raise risks at the un-targeted organisms in the environment. A novel and sustainable

strategy for improving the antimicrobial efficiency of pesticides while simultaneously

minimizing their negative impacts on ecosystems is needed. Thus, this dissertation

describes three main objectives to comprehensively understand the transformation of Cubased

nanoparticles (NPs) as affected by root exudates in the rhizosphere, antifungal

activity of newly developed Cu-based NPs, and their roles in the enhancement of nutrient

uptake, metabolite regulation, and plant growth.

1) The effects of maize (Zea mays L.)-derived root exudates (RE) and their

components on the aggregation and dissolution of copper oxide (CuO) NPs in the

rhizosphere were investigated. In this work, RE significantly inhibited the aggregation of

CuO NPs regardless of ionic strength and electrolyte type. Furthermore, this inhibition

was correlated with the molecular weight (MW) of RE fractions. Higher MW fraction

VII

(>10 kDa) reduced the aggregation most. We also discovered that RE significantly

promoted the dissolution of CuO NPs and lower MW fraction (< 3 kDa) RE mainly

contributed to this process. The addition of 20 mg/L RE reduced the seedlings’ growth

rate to 1.89% after 7 days of exposure to 25 mg/L CuO NPs, which were significantly

lower than the control group (4.82%). Notably, Cu accumulation in plant root tissues was

significantly enhanced by 20 mg/L RE. This study provides useful insights into the

interactions between RE and CuO NPs, which is of significance for the safe use of CuO

NPs-based antimicrobial products in agricultural production.

2) To increase the antifungal efficacy against the pathogenic activity of

Gibberella fujikuroi (bakanae disease) in rice (Oryza sativa L.), we synthesized copper

sulfide (CuS) NPs at 1: 1 and 1: 4 ratios of Cu and S, and treated infected rice (Oryza

sativa L.) with CuS NPs by foliar application and seed treatment. The results showed that

treating with both types of CuS NPs at 50 mg/L at the seed stage significantly decreased

disease incidence on rice by 35.1 and 45.9%, respectively. Comparatively, CuO NPs

achieved only 8.1% disease reduction, and the commercial Cu-based pesticide Kocide

3000 had no impact on disease. Foliar-applied CuO NPs and CuS (1: 1) NPs decreased

disease incidence by 30.0 and 32.5%, respectively, which outperformed CuS (1: 4) NPs

(15%) and Kocide 3000 (12.5%). Notably, CuS (1: 4) NPs also modulated the shoot

salicylic acid (SA) and jasmonic acid (JA) production to enhance the plant defense

mechanisms against G. fujikuroi infection.

3) The third study was aimed to investigate the effectiveness of a controlled

release Cu-based nano-agrichemicals in control Fusarium oxysporum f. sp. lactucae (F.o.

lact) infection on lettuce and explore their roles in the enhancement of nutrient uptake,

VIII

metabolite regulation, and plant growth. Our study demonstrated that as compared to

commercial CuO NPs, the synthesized CuO NP-embedded hydrogels at 31 mg Cu/kg soil

and 145 mg dried hydrogel powder/kg soil had a controlled release of Cu ions that could

markedly reduce the required amounts of active components (e.g., Cu in this case).

Additionally, compared to Kocide 3000 and CuO NPs, the synthesized CuO NPembedded

hydrogels exhibited greater disease suppressing activity against F.o. lact.

Notably, CuO NP-embedded hydrogels enhanced uptake of P, Mn, Zn, and Mg, and also

increased the shoot levels of organic acids as compared to the diseased control. Increased

SA but lowered levels of JA and abscisic acid (ABA) in shoots enhanced disease

resistance.

DOI

https://doi.org/10.7275/24578531

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

Available for download on Thursday, September 01, 2022

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